In recent years, in order to implement a large display screen, image display devices of multi-display type (hereinafter, referred to as multi-display devices) in which display screens of multiple displays are sequentially arranged have been put to practical use. FIG. 14 is a diagram illustrating an example of a display screen of a multi-display device. The display screen illustrated in FIG. 14 is constituted by sequentially arranging display screens of nine displays D1 to D9, three in each of the vertical and horizontal directions. In this way, the size of the display screen can be made three times larger than the size of the original display in the vertical and horizontal directions. Such multiple-display devices can be used, for example, to introduce products at stores, to display guidance information at public space such as stations or airports, as video display devices of high-definition videoconference systems, or the like.
Besides this, for image display devices equipped with a backlight, a method for driving a display panel while controlling luminance of the backlight on the basis of an image to be displayed in each of a plurality of areas defined by dividing a display screen (hereinafter, referred to as area-active driving) is known as a method for reducing power consumption of the backlight and improving the quality of a displayed image. For example, PTL 1 discloses that a luminance ratio between rays of three primary colors is controlled individually for each light-source block in accordance with a chromaticity signal detected from a video signal in an image display device that performs area-active driving.